Three dimensional printing system that automatically removes particles from build plane

ABSTRACT

A three dimensional printing system includes a print engine, a fixture, and a controller. The print engine further includes a vessel, a light engine, and a movement mechanism. The vessel is for containing a photocurable resin and has a lower portion with a transparent sheet defining a lower surface of the vessel. The light engine is configured to project radiation up through the transparent sheet over a lateral build plane which defines a maximum addressable lateral range of the light engine. The fixture has a lower face that faces downwardly. The controller is configured to: (1) position the lower face of the fixture at the build plane, and (2) operate the light engine and movement mechanism to solidify a particle trapping sheet proximate to the transparent sheet and substantially spanning the build plane and to thereby trap particles that are present along the build plane.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority to U.S.Provisional Application Ser. No. 62/247,747, Entitled “THREE DIMENSIONALPRINTING SYSTEM THAT AUTOMATICALLY REMOVES PARTICLES FROM BUILD PLANE”by Christopher Tanner et al., filed on Mar. 28, 2017, incorporatedherein by reference under the benefit of U.S.C. 119(e).

FIELD OF THE INVENTION

The present disclosure concerns an apparatus and method for fabricationof solid three dimensional (3D) articles of manufacture from radiationcurable (photocurable) resins. More particularly, the present disclosureimproves the quality of a three dimensional (3D) article of manufacturethrough the automated removal of particles from a build plane at which aphotocurable resin is being selectively solidified during fabrication.

BACKGROUND

Three dimensional (3D) printers are in rapidly increasing use. One classof 3D printers includes stereolithography printers having a generalprinciple of operation including the selective curing and hardening ofradiation curable (photocurable) liquid resins. A typicalstereolithography system includes a containment vessel holding thephotocurable resin, a movement mechanism coupled to a support surface,and a controllable light engine. The stereolithography system forms athree dimensional (3D) article of manufacture by selectively curinglayers of the photocurable resin.

In one system embodiment the vessel includes a transparent sheet thatforms part of a lower surface of the vessel. The support surface ispositioned above and in facing relation with the transparent sheet. Thefollowing steps take place: (1) The movement mechanism positions thesupport surface whereby a thin layer of the photocurable resin residesbetween the support surface and the transparent sheet. (2) The lightengine transmits pixelated light up through the transparent sheet toselectively cure a layer of the photocurable resin proximate to and ontothe support surface. The focus of the pixelated light curing is referredto a “build plane.” (3) The movement mechanism then incrementally raisesthe support surface. Steps (2) and (3) are repeated to form a threedimensional (3D) article of manufacture having a lower face in facingrelation with the transparent sheet.

One difficulty is an accumulation of particles on the transparent sheetand/or within the photocurable resin. The particles are formed from thephotocurable resin and are the result of portions of a fabricatedarticle that may break off and settle into the resin. A required gapbetween the build plane and the transparent sheet is very small. Thelower face of the support surface or three dimensional article ofmanufacture must therefore be positioned very close (a small fraction ofa millimeter typically) to the transparent sheet in order to performstep (2) above. During this positioning, the accumulated particles canbecome compressed between the transparent sheet and the lower face.These particles can be compressed and can damage the transparent sheetand become embedded in the three dimensional article of manufacture,possibly creating a defect. Damage to the transparent sheet will affectits light transmissive properties and therefore impact the quality ofall subsequent fabrication. The transparent sheet is also expensive anddisruptive to replace. What is needed is a system and method to preventthe particle accumulation and facilitate their automated removal.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram schematic of an exemplary embodiment of athree dimensional printing system for forming a three dimensionalarticle of manufacture.

FIG. 2A is a block diagram schematic depicting a print engine and afirst embodiment of a configuration whereby the print engine trapsdeleterious particles.

FIG. 2B is a block diagram schematic depicting a print engine and asecond embodiment of a configuration whereby the print engine trapsdeleterious particles.

FIG. 2C is a block diagram schematic depicting a print engine and athird embodiment of a configuration whereby the print engine trapsdeleterious particles.

FIG. 3 is a plan view schematic of an exemplary fixture for supporting aparticle trapping sheet.

FIG. 4 is a sectional view taken from AA′ of FIG. 3 with an exemplaryparticle trapping sheet included.

FIG. 5 is a schematic plan view of an exemplary particle trapping sheet.

FIG. 5A is a cross sectional view of an exemplary particle trappingsheet taken through BB′ of FIG. 5. This particle trapping sheetembodiment corresponds to FIG. 2A.

FIG. 5B is a cross sectional view of an exemplary particle trappingsheet taken through BB′ of FIG. 5. This particle trapping sheetembodiment corresponds to FIG. 2B.

FIG. 6A is a flowchart depicting a first embodiment of a process foroperating printing system 2 which corresponds to FIG. 2A.

FIG. 6B is a flowchart depicting a second embodiment of a process foroperating printing system 2 which corresponds to FIG. 2B.

FIG. 6C is a flowchart depicting a third embodiment of a process foroperating printing system 2 which corresponds to FIG. 2C.

SUMMARY

In a first aspect of the disclosure, a three dimensional printing systemincludes a print engine, a fixture, and a controller. The print enginefurther includes a vessel, a light engine, and a movement mechanism. Thevessel is for containing a photocurable resin and has a lower portionwith a transparent sheet defining at least part of a lower surface ofthe vessel. The light engine is configured to project radiation upthrough the transparent sheet over a lateral build plane which defines amaximum addressable lateral range of the light engine. The fixture has alower face that faces downwardly. The controller is configured to: (1)position the lower face of the fixture at the build plane which is at anoperating distance from the transparent sheet, and (2) operate the lightengine and movement mechanism to solidify a particle trapping sheetproximate to the transparent sheet and substantially spanning the buildplane and to thereby trap particles that are present along the buildplane.

In one implementation the controller includes a processor coupled to aninformation storage device. The information storage device includes anon-transient or non-volatile storage device storing instructions that,when executed by the processor, control the light engine and themovement mechanism. The controller can be at one location or distributedamong a plurality of locations in the printing system. In a firstembodiment the controller is entirely within the print engine whichoperates as a standalone three dimensional printer. In a secondembodiment the controller includes a control server that controls theoverall printing system and a print engine controller that is locatedwithin the print engine. In the second embodiment the three dimensionalprinting system includes various modules including one or more of afixture cassette, a post processing station, an inspection station, anda robotic transport mechanism for transporting the fixture between themodules.

In another implementation the fixture has a lower end defining arecessed surface from which a plurality of projections extend downwardlyfrom the recessed surface to distal tips. The particle trapping sheetdefines an upper surface coupled to the distal tips and an opposed lowersurface. The opposed lower surface further defines a plurality oftapering features. The controller is further configured to operate thelight engine and the movement mechanism to form a three dimensionalarticle of manufacture that is coupled to the tapering features. Thetapering features minimize a surface area of connection between thethree dimensional article of manufacture and the particle trapping sheetin order to facilitate the later physical separation of the particletrapping sheet from the three dimensional article of manufacture.

In yet another implementation the printing system includes a transportmechanism and the controller is further configured to: (3) unload thefixture from the print engine, (4) load a new fixture into the printingsystem, and (5) operate the light engine and the movement mechanism toform a three dimensional article of manufacture. The fixture used insteps (1) and (2) is a disposable fixture that is used exclusively forforming the particle trapping sheet and removing particles. Thedisposable fixture has a lower end defining a recessed surface fromwhich a plurality of projections extend downwardly from the recessedsurface to distal tips. An upper surface of the particle trapping sheetis formed onto the distal tips. The fixture used in steps (3) to (5) isa reusable fixture that is used entirely for forming three dimensionalarticles of manufacture.

In a further implementation the controller is configured to operate thelight engine and the movement mechanism to form a three dimensionalarticle of manufacture onto the fixture before forming the particletrapping sheet. The particle trapping sheet includes a plurality ofupwardly extending extensions that form a framework for supporting theparticle trapping sheet onto the three dimensional article ofmanufacture.

In a yet further implementation the particle trapping sheet has an uppersurface and an opposed lower surface. The particle trapping sheetdefines at least one opening passing from the upper surface to theopposed lower surface to provide flow of photocurable resin therethroughwhen the movement mechanism is raising or lowering the fixture.Preferably the at least one opening includes an array or plurality ofopenings that are laterally distributed across the particle trappingsheet.

In another implementation the particle trapping sheet includes a thinparallelepiped portion covering most or essentially all of the lateralarea of the build plane. The thickness is minimized so as to minimize arequired amount of resin for fabricating the particle trapping sheet.The particle trapping sheet also includes a framework of ribs orthickened portions to provide mechanical support for the thinparallelepiped portion. In some embodiments the particle trapping sheetincludes tapering features and/or extensions for coupling to a threedimensional article of manufacture. The coupling occurs at a narroweddistal tip. The tapering features and/or extensions can be laterallyaligned with the ribs so as to improve structural integrity. The thinparallelepiped portion can define openings therethrough to allow a flowof photocurable resin therethrough to facilitate vertical movement ofthe fixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram schematic of an exemplary embodiment of athree dimensional printing system 2 for forming three dimensionalarticles of manufacture. Three dimensional printing system 2 includesfixture cassettes 4, print engines 6, post-processing stations 8,inspection stations 10, a transport mechanism 12, and a control server14.

A fixture cassette 4 stores a stack of fixtures that are utilized inprint engine 6, post-process stations 8, and inspection station 10. Insome embodiments there are different fixtures stored in differentfixture cassettes 4. One stack of fixtures can be disposable andutilized for a particle removal process. Another stack of fixtures canbe reusable and utilized for the formation and transport of a threedimensional article of manufacture.

An embodiment of print engine 6 will be described in further detail withrespect to FIGS. 2A, 2B, and 2C. Post process stations 8 are for addedprocesses for a three dimensional article of manufacture after it isformed. Post processing stations can include rinsing and cleaningstations, drying stations, and curing stations, to name some examples.Inspection stations 10 can be utilized to inspect for defects and/or tomeasure critical dimensions for a three dimensional article ofmanufacture after fabrication and post processing is complete.

Transport mechanism 12 is configured to pick up a fixture from a fixturecassette 4 and to transfer it to a print engine 6. Transport mechanism12 also transfers the fixture to the post process stations 8 and to theinspection stations 10. In one embodiment, the transport mechanismincludes a robotic gripper that can move in three axes.

FIG. 2A is a schematic block diagram depicting print engine 6 and afirst embodiment through which print engine 6 removes deleteriousparticles. In this and other figures, mutually perpendicular axes X, Yand Z will be used. Axes X and Y are lateral axes. In some embodiments Xand Y are also horizontal axes. Axis Z is a central axis. In someembodiments Z is a vertical axis. In some embodiments the direction +Zis generally upward and the direction −Z is generally downward.

Print engine 6 includes a vessel 16 containing photocurable resin 18.Vessel 16 includes a transparent sheet 20 that defines at least aportion of a lower surface 22 of vessel 16. A light engine 24 isdisposed to project light up through the transparent sheet 20 toselectively cure the photocurable resin 18 during formation of a threedimensional article of manufacture 26. Light engine 24 includes lightsource 28 and spatial light modulator 30.

Between a lower face 32 of the three dimensional article of manufacture26 and the transparent sheet 20 is a thin layer 34 of photocurable resin18. As the light engine 24 operates, a portion of the thin layer 34 ofphotocurable resin 18 is cured and solidified at and proximate to abuild plane 36. Build plane 36 defines a lateral extent (along X and Y)of a layer of photocure resin that the light engine 24 is capable ofcuring when forming the three dimensional article of manufacture 26.

Print engine 6 also includes a vertical movement mechanism 38 coupled toa fixture 40. Fixture 40 is for supporting the three dimensional articleof manufacture 26. Fixture 40 includes a lower end 42 having an upwardlyrecessed surface 44 and projections 46 that extend downwardly from therecessed surface 44.

Print engine 6 includes print engine controller 48 that is under controlof control server 14 and is coupled to light engine 24 and to verticalmovement mechanism 38. In the illustrated embodiment, the print enginecontroller 48 controls the light engine 24 and the movement mechanism 38to form a particle trapping sheet 50 before forming the threedimensional article of manufacture 26. The particle trapping sheet 50 isfirst formed at and proximate to the build plane 36 and just above thetransparent sheet 20. During formation of the particle trapping sheet 50the deleterious particulates are “bound up” in the particle trappingsheet 50 so that they are removed from the vicinity of the transparentsheet 20 to prevent build-up of particles and subsequent damage. Thelateral extent of the particle trapping sheet 50 is preferablysubstantially the entire build plane 36.

The particle trapping sheet 50 includes tapering features 52 that taperbetween the particle trapping sheet 50 and the three dimensional articleof manufacture 26. These tapering feature 52 facilitate removal of theparticle trapping sheet 50 from the three dimensional article ofmanufacture 26 after processing is complete.

FIG. 2B is a schematic block diagram depicting print engine 6 and asecond embodiment through which print engine 6 removes deleteriousparticles. In comparing FIGS. 2A and 2B, like reference numeralsindicate like elements. The discussion for FIG. 2B will be limited tothose features that necessarily make it different than FIG. 2A.

In the illustrated embodiment of FIG. 2B, the print engine controller 48controls the light engine 24 and the movement mechanism 38 to form athree dimensional article of manufacture 26 before forming a particletrapping sheet 50. The particle trapping sheet 50 includes extensions 54that form a framework for coupling the particle trapping sheet 50 to thethree dimensional article of manufacture 26. As with FIG. 2A, theparticle trapping sheet 50 preferably covers the entire build plane 36of light engine 24.

FIG. 2C is a schematic block diagram depicting print engine 6 and athird embodiment through which print engine 6 removes deleteriousparticles. In comparing FIGS. 2A, 2B, and 2C, like reference numeralsindicate like elements. The discussion for FIG. 2C will be limited tothose features that necessarily make it different than FIGS. 2A and 2C.

In the illustrated embodiment of FIG. 2C, the fixture 40 is a disposablefixture 40 that is used entirely for forming the particle trapping sheet50 to remove the deleterious particles. Other than being disposable, thefixture 40 is similar to the fixture 40 illustrated with respect to FIG.2A and includes the upwardly recessed surface 44 from which theprojections 46 extend downwardly.

FIG. 3 is a plan view schematic of fixture 40 looking upwardly in the +Zdirection. The fixture 40 is shown having a recessed surface 44 fromwhich projections 46 extend in the downward −Z direction. While theillustrated embodiment depicts nine projections 46 it is to beunderstood that any number of projections 46 can be employed. The use ofclosely spaced projections 46 can allow a reduction in the thickness andrigidity of the particle trapping sheet 50 because an unsupporteddistance is thereby reduced. The fixture 40 also includes openings 56for allowing the photocurable resin 18 to pass through the fixture 40 asit is raised and lowered in the vessel 16.

FIG. 4 is a cross-sectional view of fixture 40 taken through AA′ of FIG.3. FIG. 4 also includes the particle trapping sheet 50 which has beenformed onto the projections 46 of the fixture 40. The projections 46taper in downward −Z direction toward a distal end 58. Having a distalend 58 with a smaller cross sectional area reduces the impact of theprojections 46 upon particles that are proximate to the transparentsheet 20.

FIG. 5 is a schematic plan view of an exemplary particle trapping sheet50. FIG. 5A is a cross section of a first embodiment of the particletrapping sheet 50 that corresponds to the embodiment depicted in FIG.2A. The particle trapping sheet 50 includes a thin parallelepipedportion 60 covering most or essentially all of a lateral area of thebuild plane 36. Minimizing the thickness of the thin parallelepipedportion 60 minimizes an amount of photocurable resin required tofabricate the particle trapping sheet 50. The particle trapping sheet 50also includes thicker sections or ribs 62 that form a frame forsupporting the thin parallelepiped portion 60. The particle trappingsheet 50 also includes tapering features 52 for attachment to the threedimensional article of manufacture 26. The tapering geometry of thetapering features 52 minimizes a lateral area of contact between theparticle trapping sheet 50 and the three dimensional article ofmanufacture 26 to facilitate their later separation. The taperingfeatures 52 are preferably laterally aligned with ribs 62 to improvestructural integrity. The thin parallelepiped portion 60 also definesopenings 64 that allow the flow of the photocurable resin 18 as theparticle trapping sheet 50 is raised or lowered in the vessel 16. Inthis embodiment the particle trapping sheet 50 is attached to thefixture 40 at an upper side and to the three dimensional article ofmanufacture at a lower side defined by the tapering features 52 as inFIG. 2A.

While only a few openings 64 are shown, it is to be understood that alarge number of such openings 64 can be defined. The openings can beangled or stepped whereby particles are trapped at the lateral positionsof the openings 64. With a large number of openings 64, they can have arelatively small lateral dimensions to further enhance particle trappingin their vicinity.

FIG. 5B is a cross section of a second embodiment of the particletrapping sheet 50 that corresponds to the embodiment depicted in FIG.2B. In comparing the embodiment of FIGS. 5A and 5B, like element numberscorresponding to like features. Therefore this discussion will focus ondifferences. The illustrated particle trapping sheet 50 includesextensions 54 for coupling the particle trapping sheet 50 to a lowerside of the three dimensional article of manufacture 26. The extensions54 may vary greatly in a vertical extent in Z according to a geometry ofthe three dimensional article of manufacture 26. Distal ends 66 of theextensions 54 are of a minimal cross sectional area to facilitate theseparation of the particle trapping sheet 50 from the three dimensionalarticle of manufacture 26. Preferably the extensions 54 are laterallyaligned with ribs 62 to improve structural integrity.

FIG. 6A is a flowchart depicting a process 70 for operating printingsystem 2 to fabricate a three dimensional article of manufacture 26. Allsteps of this process are executed by control server 14 and print enginecontroller 48 that control portions of printing system 2 and printengine 6. Process 70 corresponds to the description of FIG. 2A.

According to step 72, the transport mechanism 12 retrieves a fixture 40from a fixture cassette 4 and loads it into a print engine 6. Thefixture 40 is an embodiment similar to that discussed with respect toFIG. 2A, FIG. 3, and/or FIG. 4. Upon loading the fixture 40 into printengine 6, the movement mechanism 38 can engage and vertically positionthe fixture 40.

According to step 74, the movement mechanism 38 lowers and positions thefixture 40 whereby the distal ends 58 of projections 46 are positionedat build plane 36. Build plane 36 is at an operating distance from thetransparent sheet 20.

According to step 76, the print engine controller 48 operates the lightengine 24 and the vertical movement mechanism 38 to form a particletrapping sheet 50 as is illustrated in FIG. 2A, FIG. 4, or FIG. 5A. Theparticle trapping sheet 50 preferably spans essentially the entire buildplane 36 and is coupled to all of the projections 46. Formation of theparticle trapping sheet traps loose particles that are primarilysolidified photocurable resin. Also as part of step 76, the connectingfeatures 52 are formed that taper downwardly.

According to step 78, the print engine controller 48 operates the lightengine 24 and the vertical movement mechanism 38 to form a threedimensional article of manufacture 26 that couples to the connectingfeatures 52. A lateral cross sectional area over which the connectingfeatures 52 couple to the three dimensional article of manufacture 26 ispreferably minimized to facilitate later separation.

According to step 79, the transport mechanism unloads the fixture 40from the print engine 6 and additional processes are performed. Theseadditional processes can include post processing, inspection, andremoval of the particle trapping sheet 50 from the three dimensionalarticle of manufacture 26. In one embodiment the transport mechanism 12sequentially transfers the fixture 40 to different post process stations8 and inspection stations 10. When the particle trapping sheet 50 isremoved it separates along the lateral area between the connectingfeatures 52 and the three dimensional article of manufacture 26.

In an alternative embodiment the print engine 6 is a standalone unit andsteps 72 and 79 are performed manually. This includes manual loading andunloading of fixture 40 as well as cleaning, drying, UV curing,inspection, and removal of the particle trapping sheet 50.

FIG. 6B is a flowchart depicting a process 80 for operating printingsystem 2 to fabricate a three dimensional article of manufacture 26. Allsteps of this process are executed by control server 14 and print enginecontroller 48 that control portions of printing system 2 and printengine 6. Process 80 corresponds to the description of FIG. 2B.

According to step 82, the transport mechanism 12 retrieves a fixture 40from a fixture cassette 4 and loads it into a print engine 6. Thefixture 40 has a lower face 45 that faces downwardly.

According to step 84, the movement mechanism lowers and positions thelower face 45 of fixture 40 at the build plane 36. The build plane 36 isat an operating distance from the transparent sheet 20. According tostep 86, the print engine controller 48 operates the light engine 24 andthe vertical movement mechanism 38 to form a three dimensional articleof manufacture 26.

According to step 88, the print engine controller 48 operates the lightengine 24 and the vertical movement mechanism 38 to form a particletrapping sheet 50 as is illustrated in FIG. 2B or FIG. 5B. The particletrapping sheet 50 preferably spans the entire build plane 36. Theparticle trapping sheet 50 is coupled to the three dimensional articleof manufacture 26 via extensions 54. The extensions 54 form a frameworkfor properly supporting the particle trapping sheet 50 in the vessel 24.

According to step 89, the transport mechanism unloads the fixture 40from the print engine 6 and additional processes are performed. Theseadditional processes can include post processing, inspection, andremoval of the particle trapping sheet 50 from the three dimensionalarticle of manufacture 26. In one embodiment the transport mechanism 12sequentially transfers the fixture 40 to different post process stations8 and inspection stations 10. When the particle trapping sheet 50 isremoved it separates along an interface between the distal ends 66 ofextensions 54 and the three dimensional article of manufacture 26.

In an alternative embodiment the print engine 6 is a standalone unit andsteps 82 and 89 are performed manually. This includes manual loading andunloading of fixture 40 as well as cleaning, drying, UV curing,inspection, and removal of the particle trapping sheet 50.

FIG. 6C is a flowchart depicting a process 90 for operating printingsystem 2 to fabricate a three dimensional article of manufacture 26. Allsteps of this process are executed by control server 14 and print enginecontroller 48 that control portions of printing system 2 and printengine 6. Process 90 corresponds to the description of FIG. 2C.

According to step 92, the transport mechanism 12 retrieves a disposablefixture 40 from a fixture cassette and loads it into a print engine 6.The fixture can be an embodiment that is similar to that discussed withrespect to FIG. 2C, FIG. 3, or FIG. 4. Upon loading the fixture 40 intoprint engine 6, the movement mechanism 38 can engage and verticallyposition the fixture 40.

According to step 94, the movement mechanism 38 lowers and positions thefixture 40 whereby the distal ends 58 of projections 46 are positionedat build plane 36. Build plane 36 is at an operating distance from thetransparent sheet 20.

According to step 96, the print engine controller 48 operates the lightengine 24 and the vertical movement mechanism 38 to form a particletrapping sheet 50 as is illustrated in FIG. 2C. The particle trappingsheet 50 preferably spans essentially the entire build plane 36 and iscoupled to all of the projections 46. Formation of the particle trappingsheet traps loose particles that are primarily solidified photocurableresin.

According to step 98, the transport mechanism unloads the disposablefixture 40 from the print engine 6. According to step 100, the transportmechanism loads a new fixture 40 into the print engine 6. According tostep 102, the print engine controller 48 operates the light engine 24and the vertical movement mechanism 38 to form a three dimensionalarticle of manufacture 26.

According to step 104, the transport mechanism unloads the fixture 40from the print engine 6 and additional processes are performed. Theseadditional processes can include post processing, and inspection. In oneembodiment the transport mechanism 12 sequentially transfers the fixture40 to different post process stations 8 and inspection stations 10.

The specific embodiments and applications thereof described above arefor illustrative purposes only and do not preclude modifications andvariations encompassed by the scope of the following claims.

What we claim is:
 1. A three dimensional printing system comprising: aprint engine including: a vessel for containing a photocurable resin andhaving a lower portion with a transparent sheet; a light engineconfigured to project radiation up through the transparent sheet over abuild plane defining a maximum addressable lateral range of the lightengine; and a movement mechanism; and a fixture coupled to the movementmechanism with a lower face; and a controller configured to: (1)position the lower face of the fixture at an operating distance from thetransparent sheet; and (2) operate the light engine and movementmechanism to solidify a particle trapping sheet proximate to thetransparent sheet and substantially spanning the build plane and tothereby trap particles that are present along the build plane.
 2. Thethree dimensional printing system of claim 1 wherein a lower end of thefixture defines a recessed surface and a plurality of projectionsextending downwardly from the recessed surface to distal tips, theparticle trapping sheet is formed onto the distal tips.
 3. The threedimensional printing system of claim 2 wherein the particle trappingsheet includes an upper surface coupled to the distal tips and anopposed lower surface, the controller is further configured to operatethe light engine and movement mechanism to form a three dimensionalarticle of manufacture onto the opposed lower surface.
 4. The threedimensional printing system of claim 3 wherein the opposed lower surfaceincludes a plurality of tapering features that couple the threedimensional article of manufacture to the opposed lower surface wherebythe three dimensional article of manufacture can be separated from thetapering features along a minimal surface area.
 5. The three dimensionalprinting system of claim 2 wherein the printing system includes atransport mechanism and the controller is further configured to: (3)unload the fixture from the print engine; (4) load a new fixture intothe printing system; and (5) operate the light engine and the movementmechanism to form a three dimensional article of manufacture.
 6. Thethree dimensional printing system of claim 1 wherein the controller isconfigured to operate the light engine and the movement mechanism toform a three dimensional article of manufacture between step (1) andstep (2).
 7. The three dimensional printing system of claim 6 whereinthe particle trapping sheet includes a plurality of upwardly extendingextensions that form a framework for supporting the particle trappingsheet onto the three dimensional article of manufacture.
 8. The threedimensional printing system of claim 1 wherein the particle trappingsheet includes at least one opening passing from an upper surface to anopposed lower surface to provide flow of photocurable resin therethroughwhen the movement mechanism is raising or lowering the fixture.
 9. Thethree dimensional printing system of claim 1 wherein the particletrapping sheet includes a thin parallelepiped portion covering most ofthe lateral area of the build plane, the particle trapping sheetincludes a framework of ribs that provide mechanical support for thethinner portion.
 10. A method of operating a three dimensional printingsystem for forming a three dimensional article of manufacture, the threedimensional printing system including a resin vessel containingphotocurable resin and having a lower portion with a transparent sheet,a light engine configured to project radiation up through thetransparent sheet over a build plane defining a maximum addressablelateral range of the light engine, a movement mechanism, a fixturecoupled to the movement mechanism with a lower face, and a controller,the method including: (1) positioning the lower face of the fixture atan operating distance from the transparent sheet; and (2) operating thelight engine and movement mechanism to solidify a particle trappingsheet proximate to the transparent sheet and substantially spanning thebuild plane to thereby trap particles that are present along the buildplane.
 11. The method of claim 10 wherein a lower end of the fixturedefines a recessed surface and a plurality of projections extendingdownwardly from the recessed surface to distal tips and the particletrapping sheet is formed onto the distal tips.
 12. The method of claim11 wherein the particle trapping sheet includes an upper surface coupledto the distal tips and an opposed lower surface, the method furthercomprising operating the light engine and movement mechanism to form athree dimensional article of manufacture onto the opposed lower surface.13. The method of claim 12 wherein the opposed lower surface includes aplurality of tapering features that couple the three dimensional articleof manufacture to the opposed lower surface whereby the threedimensional article of manufacture can be separated from the taperingfeatures along a minimal surface area.
 14. The method of claim 11wherein the printing system includes a transport mechanism and themethod further comprises: (3) unload the fixture from the print engine;(4) load a new fixture into the printing system; and (5) operate thelight engine and the movement mechanism to form a three dimensionalarticle of manufacture.
 15. The method of claim 10 further comprisingoperating the light engine and the movement mechanism to form a threedimensional article of manufacture between step (1) and step (2). 16.The method of claim 15 wherein the particle trapping sheet includes aplurality of upwardly extending extensions that form a framework forsupporting the particle trapping sheet onto the three dimensionalarticle of manufacture.
 17. The method of claim 10 wherein the particletrapping sheet includes at least one opening passing from an uppersurface to an opposed lower surface to provide flow of photocurableresin therethrough when the movement mechanism is raising or loweringthe fixture.
 18. The method of claim 10 wherein the particle trappingsheet includes a thin parallelepiped portion covering most of thelateral area of the build plane, the particle trapping sheet includes aframework of ribs that provide mechanical support for the thinnerportion.